1. Field of Art
The subject matter described herein generally relates to flight planning for aircraft, and more specifically, to determining flight paths, speed, payload and fuel parameters that optimize one or more desired considerations (e.g., fuel, duration of travel) for an aircraft voyage.
2. Description of the Related Art
Flight planning has been important to air travel since before the advent of fixed-wing aircraft. Determining the range of an aircraft to deliver a given payload, the fuel required for such a trip, the bearings and altitudes to be used are all critical considerations for safe and efficient air travel.
As fuel costs continue to rise and as concern about global climate change increases, a great amount of attention has been given in recent years to efficiency in air travel. Likewise, military applications look to efficiency, not only to minimize cost of operations but also to allow existing aircraft to transport greater payloads over longer distances. Efficiency also often translates into increased useful life for individual airframes and the ability to transport more cargo between aircraft overhauls.
For example, NASA has studied whether use of staged airline voyages, rather than long-haul trips, might lead to reduced emissions resulting from air travel. See Andrew S. Hahn, Staging Airline Service, American Institute of Aeronautics and Astronautics (2007), available at ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070032063_2007032029.pdf. That paper addresses a number of analytical approaches for determining aircraft range, from the classic Breguet Range Equation to more recent approaches. Government agencies of other countries have likewise addressed similar issues. In J. Vankan, et al., Multi-Objective Optimisation of Aircraft Range and Fuel Consumption, National Aerospace Laboratory NLR (Amsterdam, the Netherlands, 2007), available at http://www.vivaceproject.com/content/advanced/57Vankan.pdf, various adjustments and corrections are applied to traditional Breguet range calculations in an attempt to achieve Pareto optimal improvements in aircraft design.
Central to many of these approaches is the recognition that an aircraft's range is based in part on its weight, which includes both the weight of the fuel it carries and of the static payload it is carrying. Recognition that a vehicle's payload capacity is related to the fuel it is carrying is not unique to aircraft; analysis of ships and land vehicles also recognizes the “fuel as payload” issue. See, e.g., U.S. Pat. No. 5,880,408 (to assignee-at-issue Caterpillar, Inc. and disclosing techniques for compensating for fuel weight in payload measurement system).
Vehicular payloads are typically static over time, in that the weight of the payload does not vary from the beginning of a voyage to the end. Fuel is an aspect of payload that is virtually unique in that it varies dramatically in weight during the voyage.
It has long been recognized that in aircraft, the varying weight of fuel is far too significant to be simply ignored, or even just averaged, in determining flight plans. Because fuel weight changes so dramatically over the course of a voyage, special computational techniques need to be used to account for the weight of fuel. In one simplistic approach, an iterative approach is used to gradually approach realistic estimation of flight characteristics such as range, endurance, and the like. Not only is such an approach inaccurate, it is computationally intensive and therefore either slow or expensive to use.
Another approach is described in U.S. Pat. No. 6,134,500 (to assignee-at-issue United Air Lines, Inc.), that uses “backward” search techniques that start by considering how much weight the plane is desired to have at the conclusion of a voyage from one point to another, and then works backward to determine how much weight it should have on descent, during cruise and finally on initial climb. Such backward processing simplifies the range of calculations needed to determine initial fuel loads and preferred airspeeds, altitudes and routing during flight.
Yet another approach to flight planning does not attempt to load enough fuel on the plane to clear all possible safety parameters for the journey from a worst-case perspective. Instead, a reasonably expected case is used for fuel loading calculations, and then divert locations are determined so that if conditions worse than expected arise, the aircraft can make an enroute determination to refuel using a “reclear” procedure. Thus, far less fuel needs to be carried than for the conventional worst-case planning technique. However, more accurate and computationally simple mechanisms than the conventional ones for determining fuel loading are still applicable to such improved approaches to flight planning
In military applications, another factor to be considered is the availability of in-flight refueling. Such refueling allows aircraft to take off with lighter fuel loads (and therefore heavier static payloads) than would normally be possible, or to take off in shorter distances than would be possible with full fuel tanks Determining where and how often to refuel to minimize cost can have dramatic impacts on overall mission costs.
Commonly owned U.S. Pat. No. 8,010,242 addresses a number of these issues by including an initial, intentionally false assumption that the entire gross payload capacity of a plane is used for fuel. This assumption is used to seed an initial set of legal routes, after which an assumption is made that some fuel is removed, remaining legal routes are re-calculated, and so on until results are achieved that permit the desired amount of actual (i.e., non-fuel) payload to be placed on the aircraft.
In spite of the long-understood need to consider fuel weight in flight planning, there remains a need for a computationally simple approach to help in determining factors such as flight path, fueling logistics and the like. Recently, the complexity of such planning has increased as additional parameters have been requested by aircraft operators. For instance, there is now interest in optimizing among fixed payload requirements, fuel requirements, ground track, altitude and speed. The first two factors are often selected initially as constraints, leaving the task as the optimum search within the four remaining dimensions. No quantitative methods exist that permit simple yet efficient determination of such factors.